The present invention relates to space heaters and, more particularly, to a device and method for producing infrared radiation to heat the surrounding area.
The most common way to heat the contents, such as people, of a restricted space, such as a chilly room, is to heat the air within that space. A more efficient way of achieving the same results is to direct infrared radiation at the targets to be heated, as well as at surfaces such as walls and floors in the restricted space, thereby eliminating the need to use warm or hot air as an intermediary. The targets and the irradiated surfaces then become an ensemble of low-temperature radiant re-emitters. Because infrared energy is absorbed solely where it is directed, it is possible to divide the restricted space into separate smaller zones and to maintain a different comfort level in each zone. Objects in contact with the floor are warmed both by direct radiation and by conduction from the floor. This method of space heating has been applied to a wide variety of locations, including warehouses, garages, greenhouses, transportation terminals, airplane hangers, gymnasia, tennis courts, farm and industrial buildings and loading docks.
The most common way to generate the infrared radiation is by using a gas radiant tube heater, as illustrated schematically in FIG. 1. The components of a conventional gas radiant tube heater include a radiant tube 10, a control and combustion system 12, a fuel inlet 14, an air inlet 16, an exhaust fan 18 and a reflector 20. A gaseous hydrocarbon fuel such as methane is introduced to control and combustion system 12 via fuel inlet 14. Air, as a source of oxygen, is introduced to control and combustion system 12 via air inlet 16, which may be as simple as a hole in the side of control and combustion system 12. Control and combustion system 12 ignites the resulting air-fuel mixture at the left end of radiant tube 10, producing hot reaction products, which, when they contact the inner wall of radiant tube 10, are at a temperature of about 500.degree. C. at the left end of radiant tube 10 and at a temperature of about 150.degree. C. at the right end of radiant tube 10. These reaction products ideally include only water vapor and carbon dioxide, but often also include carbon monoxide, soot and nitrogen oxides. Exhaust fan 18 pulls these reaction products through radiant tube 10, heating radiant tube 10 and causing radiant tube 10 to emit infrared radiation. Reflector 20 directs this infrared radiation in the desired direction. For example, if the gas radiant tube heater of FIG. 1 were mounted on the ceiling of a room, reflector 20 would be positioned as shown to direct the infrared radiation downward. An illustrative example of a gas radiant tube heater may be found in U.S. Pat. No. 5,429,112, to Rozzi.
Structurally, the only requirement that must be satisfied by radiant tube 10 are that it be sufficiently sturdy to withstand the temperatures generated therewithin by the hot products of the combustion of the fuel in the atmospheric oxygen. Preferably, the outer surface of radiant tube 10 is treated to promote efficient emission of infrared radiation, for example by painting the outer surface of radiant tube 10 black, using a high temperature black paint. Typically, radiant tube 10 is a cylinder from 3 meters to 30 meters in length and from 4 inches to 6 inches in diameter, although other shapes are used. For example, the radiant tube of the Rozzi patent is U-shaped. Typically, the temperature of the outer surface of radiant tube 10 reaches an operating temperature of between 400.degree. C. at the left end of radiant tube 10 and 100.degree. C. at the right end of radiant tube 10.
Conventional gas radiant heaters suffer from the following limitations:
1. Fuel and air must be introduced to control and combustion system 12 in near-stoichiometric proportions. The resulting mixture may explode in case of heater malfunction.
2. As noted above, the reaction products often include pollutants such as carbon monoxide, soot and nitrogen oxides.
3. The relevant components of control and combustion system 12 and radiant tube 10 (for example, the left end of radiant tube 10 where the combustion takes place) must be sufficiently sturdy to withstand the combustion temperatures of between 1300.degree. C. and 1900.degree. C.
4. Because of the temperature drop along radiant tube 10, the infrared radiation is emitted inhomogeneously.
The invention of the Rozzi patent cited above was directed specifically at limitations numbers 1 and 3. Limitations numbers 2 and 4 are inherent to conventional gas radiant heaters.
There is thus a widely recognized need for, and it would be highly advantageous to have, a design for gas radiant heaters that would overcome the disadvantages of presently known systems as described above.